The three best 1Tb consumer priced drives for that NAS would be WD Caviar Black, Samsung Spinpoint F3 and Hitachi Deskstar 7K1000. Best to get all drives the same at the same time. You can check individual reviews on each, they are all excellent. I've used them all in many NAS builds and never had issues with any. While the benchmarks vary a bit, they all perform comparably in service.